Background

Met Mast Removal (Decommissioning): Ijmuiden Ver Wind Farm

Background

Through a strong existing relationship Proserv was contracted by the client to provide met mast removal services as part of a wind farm decommissioning workscope. The client required a solution for the removal of a met mast structure within the Ijmuiden Ver wind farm located in the Southern North Sea, Dutch Sector. In order to complete the work scope Proserv designed bespoke tooling solutions to overcome the engineering challenges offshore.

Background

Solution

Proserv provided site survey services and engineered and manufactured bespoke cutting tooling to complete the decommissioning operations. Prior to the cutting scope and due to the size of the monopile, Proserv constructed a purpose built external circumference guideband capable of cutting up to a 10.4 metre circumference. Working closely with the client to implement modifications meant the bespoke guideband had the necessary diver friendly interfaces. Trials were carried out at Proserv’s Birchmoss Facility prior to mobilisation offshore.

Scope

The first phase of the work scope included conducting a site survey which made use of a small vessel, vessel winch and A-frame to deploy a side scan sonar and magnetometer. Seabed mapping was performed using a hull mounted multi-beam echo sounder (MBES). The survey was then performed with 5 metre line spacing and a survey speed of 4 knots, ensuring full data coverage with the monitoring of online data acquisition.

The second phase included the cutting operations which were carried out in two separate removal stages. The first consisted of the external water abrasive cut by using the purpose-built guideband that clamped round the monopile. A chain driven cutting manipulator then rotated on the guideband with an abrasive cutting nozzle severing the full 10.4 metre circumference. During the second removal phase Proserv utilised various existing tooling to complete the removal of the driven pile. A hydraulic grab tool removed 19200 kilograms of rock scour from inside the monopile which allowed an airlift tool to remove 15 metres of soil. This provided access for a second cut using an internal pipe cutter (IPC) to sever the 9.11 metre pile stub below the mudline. Proserv also provided abrasive hole-cutters for the attachment of the heavy lift rigging to allow the client to perform their 240 tonne lift of the monopile upon severance which completed the decommissioning workscope.

Background

Benefits

  • Bundled service allowing the client to source fewer contractors to complete the decommissioning scope
  • Cross utilisation of personnel and equipment allowed for reduced personnel on board and overall cost and time savings
  • Early engagement and collaboration with the end client and sub-contractors allowed for a better understanding of project challenges and parameters allowing for safe and efficient operational execution on time and on budget

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